Activated carbon fibers are generally produced by a manufacturing sequence comprising a step of spinning a carbonaceous precursor material, such as pitch, to prepare a fiber aggregate, a step of infusiblizing the fiber aggregate to render it heat-resistant, and a step of activating the thus-infusiblized fiber aggregate to generate therein a multiplicity of micropores adapted to absorb various substances. Regarding the production technology for such activated carbon fibers, Japanese Patent laid open No. 255516/1990 discloses a method in which the spinning of pitch, and the infusiblization and activation of a carbon aggregate are performed in a continuous sequence.
In the above manufacturing technology and equipment for the production of activated carbon fibers, each of the constituent steps or stages is closely associated with the performance of the final activated carbon fiber. Therefore, the degree of treatment in any one stage has a profound influence on the subsequent stages and, hence, on the performance of the product activated carbon fiber. In other words, the conditions of treatment in each stage must be critically controlled.
Meanwhile, in the production of activated carbon fibers, the infusiblization and activation of the fiber aggregate are conducted at comparatively high temperatures and, therefore, may cause various problems. Thus, in order to control the infusiblization and activation temperatures, it is necessary to supply a thermal energy corresponding to the loss of heat due to dissipation and deprivation by the infusiblization and activation waste gases in the infusiblization and activation stages.
Japanese Patent laid open No. 177217/1987 discloses a infusiblizing furnace for infusiblizing continuously carbon fiber aggregate comprising a plurality of multistage gas permeable conveyers disposed in the horizontal direction within a furnace, which adjoining conveyers can be traveled in the traverse direction each other and the terminal ends of the adjoining conveyers are shifted by a predetermined distance in horizontal direction, walls for isolating the multistage conveyers and having a controlling mechanism for controlling a flow rate of ascending current, and a means for controlling a temperature of the multistage compartments independently. This literature also discloses that a preheated air may be supplied to the multistage compartments from the below portion of the furnace.
However, since the amount of such dissipated and deprived heat is fairly large, it is impossible to accurately control the treating temperatures in the infusiblization and activation stages by means of a burner or equivalent means. Moreover, in order to supply the thermal energy corresponding to said dissipated and deprived heat, it is necessary to install some other heat source but this entails a substantial additional capital investment.
Furthermore, when a pitch-type fiber is infusiblized, its tar fraction is vaporized. Pitch, in particular, has a tar fraction generally containing aromatic condensed polycyclic compounds with a broad molecular weight distribution so that it releases large quantities of tar. The tar fraction not only sticks to the internal surface of the infusiblizing unit but tends to plug the infusiblization waste gas pipeline. Moreover, since the tar fraction adversely affects the infusiblization reaction, the concentration of this fraction must be controlled below a certain critical value. In addition, if the infusiblization waste gas containing the tar fraction is exhausted from the system, contamination of the working area and ambient environment is inevitable.
Moreover, in the progress of activation, not only a tar fraction but a combustible mixed gas containing carbon monoxide, hydrogen, etc. is stoichiometrically produced. If the mixed gas is allowed to accumulate in the system, there may occur an explosion or, if it leaks out from the system, cause poisoning and pollution problems. Moreover, since the mixed gas exerts an adverse effect on the activation reaction, the concentration of the byproduct mixed gas must be controlled below a certain value.
Furthermore, in order to remove the tar fraction and combustible mixed gas, it is necessary to provide a collector means for trapping the tar components and an eliminating or treating device for disposal of the combustible mixed gas, with the result that the load on the plant is also increased.